1. Field of the invention
This invention relates to an improvement in an optical system of a laser beam reader for irradiating a laser beam to an object and receiving a beam of light reflected by the object to detect differences in reflectance.
2. Description of the Prior Art
A reader of this type is known, e.g., a pen type bar code reader is known.
The components of an optical system of a conventional pen type bar code reader is schematically shown in FIG. 6. In the figure, reference numeral 1a denotes a casing of a bar code reader. Within the casing 1a, a light emitting diode (LED) 2 acting as a light source and a light receiving element 3 are disposed. Light emitted by the LED 2 illuminates a bar code pattern (not shown) as a reading object through a converging element 4 and is then reflected by the bar code pattern to be made incident into the casing 1a again through the converging element 4. A part of the reflecting light, which has been made incident into the casing 1a, is guided to the light receiving element 3 through an optical fiber 5.
When the bar code pattern is read, the bar code pattern is contacted with the converging element 4 and in that state, the bar code pattern is scanned by the reader. By this, there can be detected information which the bar code pattern has in accordance with the changes in reflectance of the bar code pattern due to the scanning.
However, the above-mentioned bar code reader has an extremely narrow readable range. Therefore, when the converging element 4 and the bar code pattern are separated from each other, it becomes impossible to read the bar code pattern. Therefore, in case a printed surface of the bar code pattern is not smooth, e.g., in a case in which the pattern is printed on a flexible bag or the like, the converging element 4 and the bar code pattern are readily separated during scanning due to unevenness produced on the printed surface. As a result, it becomes impossible to read such bar code pattern.
The present invention has been developed in view of the above-mentioned problems. It is therefore the object of the present invention to provide an optical system for a laser beam reader which is capable of detecting information of a reading object even if the object is separated from it during the reading.